1. Field of the Invention
The present invention relates to a stereoscopic image generating apparatus and, more particularly, to a stereoscopic image generating apparatus for generating a stereoscopic image which can be easily observed by an observer.
2. Description of the Related Art
As a conventional technique for generating a stereoscopic image using a computer, there is known a method of sensing the images of a plurality of objects located in a virtual three-dimensional space, using left and right virtual cameras located in the virtual three-dimensional space, to generate three-dimensional images in accordance with a CG (Computer Graphics) technique disclosed in, e.g., "3-D CG", edited by the Institute of Television in Japan, Ohm Publishing Company, pp. 1-27, 1994.
According to this method, left and right two-dimensional images having a parallax are obtained. At the same time, to create a stereoscopic moving picture, an object is moved with time with respect to the left and right virtual cameras fixed in the virtual three-dimensional space, or the left and right virtual cameras are moved with time with respect to a plurality of fixed objects, thereby obtaining a plurality of images which constitute a stereoscopic moving picture.
FIG. 27 is a flow chart for explaining the conventional stereoscopic image creating method using the CG technique.
In steps 101 to 103 of FIG. 27, the shape data, initial position data, and time movement data (motion data) of a plurality of objects are input and stored in an external storage device.
In step 104, the position data, field angle data, and crossing angle (posture) data of the left and right virtual cameras are input and stored in the external storage device.
In steps 105 and 106, generation (rendering) of left and right two-dimensional images is performed for all frames on the basis of the data stored in steps 101 to 104.
Assume that a ball 2 and a trigonal pyramid 3 which serve as objects, and left and right virtual cameras 4L and 4R are located in a virtual three-dimensional space 1, as shown in FIG. 28, and that the ball 2 is moved to come close to the left and right virtual cameras 4L and 4R. In the processing of steps 101 to 106, the ball 2 is moved to the right in the left image and to the left in the right image while being enlarged when the ball 2 comes closer to the cameras, thereby forming an array of left images and an array of right images, as shown in FIGS. 29A and 29B.
The left and right image arrays thus generated are read out in steps 107 and 108, respectively. The images are stored in the order (time serial order) of, e.g., FIGS. 29A, 29B, and 29C.
These left and right image arrays are recorded on a recording medium such as a video tape using an image recording device such as a video deck.
The resultant stereoscopic image is observed on a stereoscopic display.
A head-mounted display (HMD) as one of the stereoscopic displays used for stereoscopic image observation is a kind of two-eye stereoscopic display. The left and right display elements and the left and right eyepiece optical systems are located in front of the left and right eyeballs of an observer, respectively. A left eye image is presented to the left eyeball, and a right eye image is presented to the right eyeball, so that the observer can observe the presented images as a stereoscopic image.
The observation order of the objects in the images with, e.g., the HMD in the order of the array of images in FIGS. 29A, 29B, and 29C is shown in FIG. 30.
That is, the ball 2 in FIG. 30 is moving in a direction indicated by an arrow with the lapse of time to be enlarged or popped up toward the eyeballs of the observer.
In this case, since the visual range of the images is determined by the eyepiece optical systems of the HMD, the focusing action of the eyeballs of the observer is set in the fixed state.
That is, the visual range does not coincide with the vergence distance with reference to the ball 2 in the image.
This phenomenon also occurs in various stereoscopic television systems such as a shutter switching system and a reticular system in addition to the HMD.
The visual range in such a stereoscopic television system is a distance from a display device such as a CRT (Cathode-Ray Tube) to the eyeballs of the observer.
The visual range in the HMD is a distance from each of the virtual image planes generated by the eyepiece optical systems to a corresponding one of the eyeballs of the observer.
In stereoscopic image observation, when the observer observes images whose pop-up amounts are large while the visual range does not coincide with the vergence distance, since the resultant stereoscopic image is unnaturally observed, there is a case of resulting in asthenopia due to the observer.
To solve this problem, images whose change in pop-up amount is small are generated. In this case, however, the stereoscopic image impression given to the observer is weakened.
To solve the above problem, Jpn. Pat. Appln. KOKOKU Publication No. 6-85590 discloses a technique for mechanically driving eyepiece lenses of the HMD in stereoscopic image observation to change the visual range in accordance with the generated images.
In this technique, a device for "mechanically driving the eyepiece lenses" must be added to the HMD, inevitably resulting in an increase in cost.